Natural resources such as gas, oil, and water residing in a geological formation may be recovered by drilling a wellbore into the formation while circulating a drilling fluid in the wellbore. After terminating the circulation of the drilling fluid, a string of pipe (e.g., casing) is run into the wellbore in order to provide structural support for the wellbore sides. A cement slurry is injected into the annulus between the casing and the geological formation. The hardened cement seals the annulus and supports the string of pipe in the wellbore.
Tools (e.g., acoustic, electromagnetic) may be lowered into the wellbore casing to determine properties of deposits (e.g., fluids, gas) in the geological formation. In order to provide more accurate results for these measurements, it can be useful to know the distance between the tool and the casing, as well as the density of material within the casing.